On Iran—unlike almost any other national security issue—Trump has overseen something like a policy debate, arriving at something like an intermediate position. The Iran deal will not be canceled, it will be continued. At the same time, new actions will be taken to deal with urgent U.S. security concerns that the deal ignored.

Since the deal went into effect in mid-2015, some of its U.S. authors’ hopes have been realized; other hopes disappointed. The rulers of Iran did surrender most of its enriched uranium stockpile. They submitted at least in theory to nuclear inspections.

But in other crucial respects, the Iranian regime’s behavior has become more aggressive and more dangerous. The deal returned tens of billions of frozen assets—including upwards of $1 billion in literal cash—to the Islamic Republic. That money has helped fund a radical increase in Iran's military budget. The Iranian state has accelerated its testing of ballistic missiles. It has fought—and nearly won—a war in Syria to save its client Bashar al-Assad. Its surrogates in Yemen have begun firing missiles into Saudi Arabia, and Iranian-backed militias inside Syria are moving closer to the borders of Jordan and Israel—reportedly 10 kilometers away from the Golan Heights.

Critics of the deal have accepted that, however strongly they opposed entering into it, once entered, the costs of exiting will be too high. In a tough speech to the Council on Foreign Relations on October 3, the deal’s foremost congressional critic—Senator Tom Cotton of Arkansas—specifically repudiated recession of the deal. “Instead of that backward-looking step, which the president also has in his power to do right now, let me suggest that we look to the future and a new approach.”

The new approach Cotton has urged—and that the Trump administration contemplates—is to threaten new contingent sanctions on Iran if it continues to aggress. Cotton identified three areas where the deal must be stiffened: It must be made permanent, rather than (as parts of it now do) sunsetting in 2025; inspections must be extended throughout Iran not just to places that were nuclear sites before 2015; and Iran’s missile programs must be limited.

Cotton is not adventuring here. He is expressing themes that command broad support within the U.S. national-security community. In a September 2015 speech at the Brookings Institution on the Iran deal, candidate Clinton explicitly promised to work with deal-skeptics like Cotton to tighten pressure on Iran—and to maintain the threat of force should the Iranian regime seek to cheat.

[I]t’s not enough just to say “yes” to this deal. Of course it isn’t. We have to say “yes, and.” “Yes, and” we will enforce it with vigor and vigilance. “Yes, and” we will embed it in a broader strategy to confront Iran’s bad behavior in the region. “Yes, and” we will begin from day one to set the conditions so Iran knows it will never be able to get a nuclear weapon, not during the term of the agreement, not after, not ever.

We need to be clear and I think we need to make that very clear to Iran about what we expect from them. This is not the start of some larger diplomatic opening and we shouldn’t expect that this deal will lead to broader changes in their behavior. That shouldn’t be a promise for proceeding. Instead, we need to be prepared for three scenarios: first, Iran tries to cheat, something it’s been quite willing to do in the past; second, Iran tries to wait us out, perhaps it waits to move for 15 years when some, but not all, restrictions expire; and, third, Iran ramps up its dangerous behavior in the region, including its support for terrorists groups, like Hamas and Hezbollah. …

My starting point will be one of distrust. You remember President Reagan’s line about the Soviets, “Trust, but verify”? My approach will be distrust and verify. We should anticipate that Iran will test the next President. They’ll want to see how far they can bend the rules. That won’t work if I’m in the White House. I’ll hold the line against Iranian noncompliance. That means penalties even for small violations; keeping our allies on board, but being willing to snap back sanctions into place, unilaterally, if we have to; working with Congress to close any gaps in the sanctions. Right now members of Congress are offering proposals to that effect and I think the current administration should work with them to see whether there are additional steps that could be taken.

But here’s where we come to the waste and risk of the Trump presidency. It’s one thing to announce a tougher policy; another to implement.

For all its sometime over-eagerness to reach a deal with Iran, the Obama administration can take credit for one great success: broad global support for its Iran sanction regime. That regime has been relaxed since 2015. To restore it will need the assent of the European Union, as well as at least some cooperation from other global powers, including China, Japan, and India—respectively the 1st, 3rd, and 4th-ranking markets for Iranian oil export before international sanctions bit.

The Trump administration has shown some ability to build international sanctions regimes when it must. It has done so against North Korea. But North Korea is not an oil exporter. Against Iran, the task will be much more difficult—and the requirement of U.S. credibility that much higher. That was Hillary Clinton’s warning in 2015:

The Iranians and the world need to understand that we will act decisively if we need to, so here’s my message to Iran’s leaders: The United States will never allow you to acquire a nuclear weapon.

As President I will take whatever actions are necessary to protect the United States and our allies. I will not hesitate to take military action if Iran attempts to obtain a nuclear weapon. And I will set up my successor to be able to credibly make the same pledge. We will make clear to Iran that our national commitment to prevention will not waiver depending on who’s in office. It’s permanent. And should it become necessary in the future, having exhausted peaceful alternatives to turn to military force, we will have preserved and, in some cases, enhanced our capacity to act. And because we’ve proven our commitment to diplomacy first, the world will more likely join us.

The Trump administration, by contrast, is not seen as a good-faith actor, never mind by America’s enemies, but also by its friends. It’s one thing to announce new plans against Iran, another and much more challenging to implement them, more challenging still to gain international support. Even when Trump speaks sense, there’s no trusting his execution of those words. The likeliest outcome is not enhanced U.S. security, but two nuclear crises at the same time, one in North East Asia and a second in the Middle East.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.